The present invention relates to a method for operating a drive device with an internal combustion engine and an exhaust tract in which a storage catalytic converter for purification of exhaust gas of the internal combustion engine, a first lambda probe upstream of the storage catalytic converter and a second lambda probe downstream of the storage catalytic converter are arranged, wherein a lambda value for controlling a mixture composition is determined for the internal combustion engine from a measurement signal of the first lambda probe and an offset value. The invention further relates to a drive device.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
The drive device is used, for example, for driving a motor vehicle or is a component of the motor vehicle. It includes at least the internal combustion engine and the exhaust tract through which exhaust gas of the internal combustion engine is discharged, in particular toward the outside of the drive device. The storage catalytic converter is disposed in the exhaust tract of, which serves to clean the exhaust gas. The storage catalytic converter is implemented, for example, in the form of NO storage catalytic converter.
The drive device has at least two lambda probes. The first oxygen sensor is disposed upstream of the storage catalytic converter, so that it can be used to measure the oxygen content in the exhaust gas at this location. The first lambda probe is for this purpose arranged such that it at least partially protrudes into the exhaust gas or is in fluid communication with the exhaust gas, for example, is overflowed by the exhaust gas. Conversely, the second lambda probe is disposed downstream of the storage catalytic converter and is thus used to determine an oxygen content in the exhaust gas at this location. Like the first lambda probe, the second lambda probe protrudes at least partially into the exhaust gas or is in fluid communication with the exhaust gas, so it is particularly overflowed by the exhaust gas. For example, the first lambda probe is designed as a broadband lambda probe and the second lambda probe is designed as a jump lambda probe.
The measurement signal of the first lambda probe is used for controlling the mixture composition for the internal combustion engine. The composition of the fuel-air mixture supplied to the internal combustion engine is thereby obtained as a function of the measurement signal of the first lambda probe. To compensate for any error, especially an offset error, of the first lambda probe, the lambda value which ultimately forms the basis for controlling the mixture composition is determined from the measurement signal of the first lambda probe and the offset value. In particular, the lambda value results from the sum of the measurement signal and the offset value. In this way, the accuracy of the control of the mixture composition can be significantly improved.
For example, the offset value can be determined based on a measurement signal from the second lambda probe, in particular in the context of a trim control. In order to carry out a conventional trim control, which counterbalances a displacement (for example, due to age) of the mean value, corresponding to lambda=1, of the signal of the lambda probe, a trim controller receives an oxygen-dependent signal from a measuring sensor, e.g. a second lambda probe, disposed downstream of the catalytic converter. The measurement signal from the second lambda probe is then used to detect and to eventually correct an error of the first lambda probe. However, since the exhaust gas downstream of the lambda probe must first pass through the storage catalytic converter before it reaches the second lambda probe, the second lambda probe reacts only very slowly to a change in the exhaust gas composition, not least due to the storage capacity, in particular the oxygen storage capacity of the storage catalytic converter. The storage catalytic converter has an oxygen store for storing or temporarily storing the oxygen.
Due to the sluggish reaction, the trim control can be performed only very slowly, i.e. with a large time constant, in order to ensure a stable control loop. However, this means that the offset value can be adjusted only very slowly to compensate for the measurement error of the first lambda probe. This measurement error thus initially causes an undesirable deviation in the mixture composition, which leads to increased pollutant emissions of the drive device.
It would therefore be desirable and advantageous to obviate prior art shortcomings and to provide an improved method for operating a drive device, which in particular enables a more reliable control of the mixture composition.